The present invention relates to a lockup unit in a torque converter, and more particularly to a lockup unit which engages a friction element which co-acts with another element fixed to the turbine of the torque converter for mechanically coupling the lockup unit and the turbine.
Torque converters are commonly used to transmit torque between the crankshaft of an internal combustion engine and an automatic transmission. A torque converter typically includes a front cover coupled to the crankshaft of the engine and is filled with an hydraulic fluid. Within the front cover are three kinds of vaned wheels, an impeller, a turbine, and a stator. The impeller is usually coupled to a front cover of the torque converter and rotates with the front cover. The turbine, which is rotatably disposed within the front cover, is usually coupled to the input shaft of the automatic transmission and rotates therewith. When torque is input from the engine to the front cover, the impeller vanes force fluid into the turbine, causing it to rotate. As a result, the torque is transmitted to the transmission. The stator remains generally stationary and serves to direct the flow of fluid between the impeller and turbine.
In at least one prior art torque converter, a lockup unit is disposed between the front cover and the turbine for selectively mechanically connecting the two. The lockup unit is composed of a disc-like piston to be brought into pressing contact with the front cover and a flexible coupling mechanism disposed between the turbine and the lockup unit for absorbing the vibrations experienced when the disc-like piston and the front cover contact one another. The flexible coupling mechanism typically includes a torsion spring or the like for absorbing a shock caused by the piston being brought into pressing contact with the front cover.
Recently, lockup units have also been provided a frictional resistance generating mechanism for the purpose of attenuating a twist vibration experienced when the lockup unit engages the front cover.
The conventional frictional resistance generating mechanism provided in the lockup unit is composed essentially of a plate member disposed between the lockup unit and the turbine, engaged to be rotatable together with the turbine, a flexible member for biasing the plate member into friction engagement with a portion of the lockup unit, and a support member for supporting the flexible member. A torque converter which incorporates a friction mechanism in its lockup unit generally has an increase in the number of the mechanical parts due to the presence of the frictional resistance generating mechanism.